A variety of pumps and motors are known. Most provide impellers, pistons or turbines to drive, or be driven by, fluid. Each of these designs have advantages and disadvantages. In some motor applications, power is lost due to a failure to adequately harness the energy of the driving fluid. In some impeller type pump applications, fluid may tend to slip past impeller vanes, particularly where the pressure differential is great. In applications using pistons, fluid is less likely to slip past the piston without driving, or being driven by the piston. However, friction between piston rings and cylinders tends to decrease efficiency of these applications.
What is needed is an apparatus that is adapted for use as a pump or motor that combines the advantages of impellers and turbines with the advantages of pistons, while minimizing the disadvantages of both.